This invention relates generally to drag type rotary drill bits and more particularly to the arrangement of cutting elements along curved blades and fluid discharge nozzles arranged in advance of the cutting elements.
It has become common practice to dress drag type rotary well drilling bits with cutting elements made of man made polycrystalline diamond compacts or cutters projecting from the bit body. This technology has allowed diamond cutting elements to be formed and shaped into more desirable cutting edges and has further provided higher strength diamonds allowing cutting edges to project a maximum distance from the bit body. One polycrystalline diamond cutting structure in common use has been what is commonly referred to as polycrystalline diamond compact (PDC) which is a small carbide plate with a thin layer of polycrystalline diamond bonded to one face. This has resulted in PDC type diamond drill bits capable of drilling more efficiently in softer formations than was possible with the natural diamonds used in earlier diamond bits.
The use of these PDC type diamond drill bits has also had resultant undesirable increased problems associated with heat degradation and "balling". Balling is a build up of formation chips or cuttings on the bit face or the hole bottom and is caused by sticky formations, such as sticky shales or similar formations having a large percentage of clays, adhering to the cutting face of the bit. This balling condition not only deters drilling, but it also causes rapid heat deterioration of the cutting elements due to poor circulation and decreased cutting efficiency.
This balling condition occurs primarily when using water based muds which cause a swelling of the clays. It is highly desirable to provide a bit dressed with these PDC type cutting elements which has the versatility to not only drill efficiently in soft, sticky formations when using water base muds, but also remain effective and durable when harder formations are encountered.
U.S. Pat. No. 4,499,958 discloses a deep bladed design for a drill bit using PDC type cutting elements but this design would appear to have a limited cleaning effect for the edges of the cutting elements. Also, this type bit may be subjected to considerable wear and breakage when harder formations are encountered because of the relatively small number of cutting elements and the relatively long projection of the cutting elements from the adjacent bit body or blade.
U.S. Pat. No. 4,505,342 discloses a PDC type drill bit which has a large number of cutting elements arranged on a large number of blades adjacent relatively shallow grooves, and has fluid nozzles directed at the well bore bottom. After the fluid impinges the well bore bottom a portion of the fluid flows at relatively low velocity through the fluid channels directing it in front of rows of cutting elements in an attempt to adequately flush all of the cutting elements and clean the hole bottom. The fluid velocity resulting in these channels is too low, however, for providing adequate cleaning of the cutting elements when drilling soft sticky formations with water base muds and prevent balling.
In other attempts to solve this severe cleaning problem resulting from soft sticky formations, U.S. Pat. Nos. 4,452,324; 4,471,845; 4,303,136; and 4,606,418 have disclosed PDC type diamond drill bits with relatively large numbers of nozzle orifices in the bit in an attempt to adequately clean all of the cutting elements on the bit. However, if the velocity and total orifice area are maintained a large number of nozzle orifices will result in orifices of a small area and this will increase the probability of clogging of some of the nozzle orifices. A reduced velocity will result in the event the total orifice area for the bit is increased and this likewise will increase the probability of clogging of the nozzle orifices.